Conventional room air conditioner systems normally employ a large double shafted motor to drive the inside (evaporator) coil fan or blower and simultaneously to drive the outside (condenser) coil fan or blower; or, less usually, two individual motors, each separately mounted: one motor driving the indoor coil fan and the other motor driving the outdoor coil fan.
There are many advantages to utilizing a unitary housing double-motor unit. As discussed below, it will be evident that some of the advantages are inherent in the flexibility of utilizing two separate motors while other of the advantages occur as a result of utilizing a unitary housing for the two separate motors.
The use of two separate motors in a unitary housing results in a saving of space, reduced noise levels, and a saving in energy. These advantages come about in a number of ways depending on the mode in which the air conditioning unit is being used and the ambient conditions under which the unit is operating.
The use of two motors permits choosing a motor which is particularly suitable for operating its associated fan. It is often advantageous to be able to vary the inside (evaporator) coil fan speed when operating the air conditioner in its usual cooling mode. Thus, when maximum cooling is not necessary, the evaporator coil fan can be slowed down, resulting in a savings in energy and in quieter operation. For some applications a smaller motor can be utilized for the inside coil fan, accomplishing a still further energy savings. If a single speed single motor with a double shaft is utilized, this variation in the speed of the evaporator coil fan is normally accomplished by utilizing a gear box when condenser fan speed must be maintained. When two motors are used, this can be accomplished by utilizing a six-pole or four-pole multi-speed motor for the evaporator coil fan and a relatively simple four-pole or six-pole single speed motor for the condenser coil fan. An arrangement incorporating two motors, each of about half the power output utilized when a single double shafted motor is employed, will take up approximately the same room as a single multi-speed motor or somewhat less room than the larger double-shafted motor with associated gear box and use less energy. Additionally, the gear-box/double-shafted motor arrangement is heavier, more expensive and noisier.
The use of two motors is also advantageous when the air conditioner unit is provided with an auxiliary electrical heating coil element for use in warming the air in a room. In this mode of operation one need only activate the inside fan, as the compressor, and therefore the condenser coil, is not being used. This, results in a savings in energy necessary to drive the fan motors as well as in a lower noise level for the unit.
In applications wherein the outside ambient temperature is extremely high, providing an air conditioning unit with an outside (condenser) coil fan of higher speed while providing the inside (evaporator) coil with a fan of lower speed can give an air conditioning unit sufficient flexibility to provide some cooling where the unit may otherwise stall from the load. A high speed outside (condenser) coil fan will increase the apparent efficiency of the compressor while a slower inside (evaporator) coil fan will simultaneously reduce the load on the compressor. Under less severe conditions this mode of operation results in more efficient operation of the unit then would otherwise be accomplished. Additionally, more comfortable cooling is provided as the unit will operate for longer periods of time at low speed thereby accomplishing extended humidity control.
A related advantage to operating an air conditioning unit in a mode wherein the outside (condenser) coil fan is operated at a higher speed is, under "normal" ambient conditions, the reduced surface area required for the outdoor (condenser) coil surface to obtain the same efficiency of operation for the compressor. This conserves materials which would otherwise be required to make a larger condenser coil surface and reduces head pressures and therefore the load or energy consumed in the compressor circuit.
As both motors are mounted in a unitary housing, aside other considerations, there is a cost reduction in materials and manpower utilized in assemblying an air conditioner unit, over using two separately mounted motors, in that both units are mounted simultaneously and require only one set of brackets, bolts, straps, or other means normally employed for mounting motors. In fact, little or no retooling costs are incurred in substituting a double-motor construction, according to the present invention, for the single motor double-shafted construction now normally utilized in air conditioners.
Some cost savings can also be realized when utilizing a single envelope construction by assemblying both motors using a single central bearing.
The double motor system described herein has been found to run cooler than the larger single motor double shafted system often utilized in the prior art, thereby contributing to the increased efficiency of this system. It may, in fact, be possible for certain combinations to utilize lower tool horsepower than was previously required by the single motor, by utilizing a lower powered indoor (evaporator) fan motor, as noted above.
It has also been found that a system according to the present invention will operate under the low line voltages normally encountered in regions where high ambient temperatures are prevalent. Prior systems utilizing a double-shafted motor have been found to stall under these conditions. Thus an air conditioner unit, according to the present invention, will not only operate more efficiency than the usual units with a double-shafted single motor, but will operate under conditions under which the usual unit will not operate at all.